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# Batteriet og elektromagnetisme

Video transcript
Consider the following experiment You have two pieces of metal: copper and zinc which you connect to conducting wires and you then submerge the metals in an electrolyte in this case vinegar You will observe that bubbles will form around the zinc but not on the copper. The metal seemed dissimilar in this way and if you then connect the two wires holding the metals, something changes. Tiny bubbles begin to form around the copper terminal. It seems as though something is being pulled from the zinc through the wire allowing a reaction to occur on the copper side and it turns out this is a flow of electrical charge as electrons are pulled away from the zinc towards the copper through the conductive path in the wire. Think of this blow as the result of a charge imbalance or electrical pressure between the two metals as compared to the instantaneous discharge observed with static electricity experiments. Towards the end of the 18th century Alessandro Volta had been investigating this effect. More importantly he found that chaining these cells together would amplify this flow of charge. And by 1800 he simplified things even further removing the jar which provided more electrolyte than was actually needed. He writes, "- A few dozen small round disks of copper, [pieces of coin for example], and equal number of plates of zinc. - I prepare circular pieces of spongy matter capable of retaining water - I continue coupling a plate of copper with one zinc and always in the same order and interpose between each of these couples a moistened disk. This continues until I have a column as high as possible without danger of it falling." This is known famously as the voltaic pile, the first battery in history to provide a continuous flow of electrical charge, or current. More cells resulted in an increased electrical pressure at the two ends and electrical pressure was an early term for what we now call voltage after Volta. Now if the two leads of a voltaic pile were brought into direct contact, a series of shocks could be observed. Now at first the utility of electric current as a communication method was not immediately obvious, aside from faint sparks and bubbles. One idea was to use the presence of bubbles to signal letters and the Bubble Telegraph used this method though it involved 26 different circuits, one for each letter and it was based on the fact that the battery providing the current can be placed at a distance away from the jars containing the leads creating the bubbles. An inventive although clumsy system which was never adopted. But very soon everything changed after a famous demonstration in 1819. It was found that if we simply pass a wire near a compass and connected to a battery as soon as the wire made contact with the battery the needle jumped without any physical contact. The only explanation was that the current carrying wire was creating a temporary magnetic field. This was followed by a series of tasks to figure out the direction of this field first we assumed it was pointing along the wire with the current or perhaps emanating outwards from the wire as heat would travel. But eventually it was deduced that it must be traveling around the wire in perpendicular circles, so a loop of wire would create a magnetic field which points through the center of the loop and around the outside. This lead to the galvanometer which was designed to detect and measure electrical current and it was just simply a coil of wire with a compass suspended in the center. Now when electric current was applied to the coil, a magnetic field would push through the middle of the coil and around the outside so the needle would always point perpendicular to the direction of the force which was balanced on either side of the needle, and the stronger the current the stronger the deflection of the needle. And by 1824 William Sturgeon demonstrated a way to increase the strength of this field even more, simply by wrapping a coil of wire around a piece of iron such as a nail the magnetic force could be amplified because iron seemed to be a better medium for supporting the formation of magnetic fields. We call this "permeability" and by wrapping the wire many times the strength of the field could be amplified thousands of times and this is known as an "electromagnet". So suddenly it was possible to create magnetic fields which could move needles with precision and force using electric current applied at a distance using a long loop of wire and a strong battery. At the time our understanding of information was in its infancy. People were thinking about information and a message as the number of letters in a message so the goal was intuitive: who could come up with the fastest way to transmit letters and whoever had the fastest system would therefore reduce the cost per message for the sender using this system. And a gold mine was waiting for whoever got there first.